JP7599459B2 - Method for producing gasoline alternative fuel and gasoline alternative fuel - Google Patents

Description

The present invention relates to a method for producing a gasoline alternative fuel using renewable energy and to a gasoline alternative fuel.

Fuel compositions as alternative fuels to gasoline have been known for some time (see, for example, Patent Document 1). The fuel composition described in Patent Document 1 has a research octane number of 89.0 or more, and contains FT synthetic base material A (50≧A>0) volume % obtained from natural gas, petroleum liquefied gas, etc., ethers B (25≧B≧0) volume % having 4 to 8 carbon atoms, and alcohols C (15≧C≧0) volume % having 2 to 4 carbon atoms (B+C>0, A≧B+C).

JP 2007-270091 A

However, since the fuel composition described in Patent Document 1 uses fossil fuels as raw materials, it is difficult to reduce the amount of carbon emissions per unit energy (carbon intensity) of the final fuel produced. From the perspective of contributing to mitigating or reducing the impact of climate change, it is desirable to reduce the consumption of fossil fuels with high carbon intensity.

One aspect of the present invention is a method for producing an alternative gasoline fuel by mixing FT light naphtha obtained by Fischer-Tropsch synthesis using renewable electricity and bioalcohol obtained from biomass to produce an alternative gasoline fuel.

The method for producing a gasoline alternative fuel includes determining a blending ratio of bioalcohol to FT light naphtha based on the octane number of the FT light naphtha, the blending octane number of the bioalcohol, and a predetermined target octane number; determining a hydrogenation ratio when hydrogenating olefins contained in the FT light naphtha to paraffins based on the determined blending ratio of bioalcohol and the olefin content ratio of the FT light naphtha so that the olefin content ratio of the gasoline alternative fuel is 10 vol% or less; hydrogenating the FT light naphtha in accordance with the determined hydrogenation ratio; and blending the bioalcohol into the hydrogenated FT light naphtha in accordance with the determined blending ratio of bioalcohol .

The present invention makes it possible to produce a gasoline alternative fuel with low carbon intensity.

FIG. 1 is a diagram for explaining renewable fuel produced using renewable energy. FIG. 2 is a diagram for explaining an octane improver. FIG. 2 is a diagram for explaining the carbon intensity of a fuel. FIG. 2 is a diagram for explaining the difference in octane number improving effect depending on the composition of the base material. FIG. 2 is a diagram for explaining differences in carbon intensity due to fuel composition. FIG. 2 is a diagram for explaining the relationship between the olefin content of the base material and the octane number improvement rate. FIG. 2 is a diagram for explaining the blending octane number of alcohol. FIG. 2 is a diagram for explaining the alcohol blend ratio required to obtain a gasoline alternative fuel. FIG. 2 is a diagram for explaining the composition of a gasoline alternative fuel according to an embodiment of the present invention. FIG. 2 illustrates a method for producing a gasoline alternative fuel according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 10. In the method for producing a gasoline alternative fuel according to an embodiment of the present invention, a gasoline alternative fuel with a low carbon strength and an octane number equivalent to that of gasoline is produced by reforming FT light naphtha with a low octane number obtained by Fischer-Tropsch synthesis using renewable electricity. In particular, a gasoline alternative fuel with an extremely low carbon strength is produced by using FT light naphtha as a base material and mixing bioalcohol as an octane number improver.

The Earth's average temperature is kept warm enough for living things by greenhouse gases in the atmosphere. Specifically, greenhouse gases absorb some of the heat radiated from the Earth's surface, which is warmed by sunlight, into space, and then re-radiate it back to the Earth's surface, thereby keeping the atmosphere warm. If the concentration of greenhouse gases in the atmosphere increases, the Earth's average temperature will rise (global warming).

Of all greenhouse gases, carbon dioxide contributes greatly to global warming. Its concentration in the atmosphere is determined by the balance between carbon fixed on the ground or underground as plants and fossil fuels, and carbon present in the atmosphere as carbon dioxide. For example, when carbon dioxide in the atmosphere is absorbed through photosynthesis during plant growth, the concentration of carbon dioxide in the atmosphere decreases, and when carbon dioxide is released into the atmosphere through the combustion of fossil fuels, the concentration of carbon dioxide in the atmosphere increases. To curb global warming, it is necessary to replace fossil fuels with renewable energy sources such as solar, wind, hydroelectric, geothermal, or biomass, and reduce carbon emissions.

Figure 1 is a diagram explaining renewable fuels (e-fuels) produced using such renewable energy. As shown in Figure 1, renewable electricity is generated by solar power generation, wind power generation, hydroelectric power generation, geothermal power generation, etc., and renewable hydrogen is produced by electrolysis of water using the renewable electricity. Furthermore, FT (Fischer-Tropsch) synthesis is performed using renewable hydrogen and carbon dioxide captured from factory exhaust gases, etc. to produce FT crude oil as e-fuel.

FT crude oil contains a variety of components due to the principle of the FT synthesis process, which is a polymerization reaction. Such FT crude oil can be fractionated according to the boiling point range and separated into FT diesel, jet fuel, and FT light naphtha as e-fuels. Of these, FT diesel can be used as fuel for diesel engines, and jet fuel can be used as fuel for jet engines as is.

FT light naphtha contains linear saturated hydrocarbons (normal paraffins) with carbon numbers of about 6 to 10 as its main component. In addition, unsaturated hydrocarbons (olefins) and aromatic hydrocarbons (aromas) are contained as secondary components in a content ratio that depends on the catalyst, reaction temperature, reaction time, etc. used in the FT synthesis process. Such FT light naphtha is suitable as a base material for gasoline alternative fuels because its vapor pressure characteristics (vaporization characteristics) comply with gasoline standards. However, FT light naphtha has an octane number (research method octane number) of about 60 to 70, which is lower than the gasoline standard (about 90), and if it is used as fuel for gasoline engines as is, knocking may occur and the combustion performance of the engine may be impaired.

Figure 2 is a diagram for explaining octane number improvers, and shows an example of the measurement results of the octane number of fuel obtained by mixing various octane number improvers with FT light naphtha (base material) with an octane number of 65. As shown in Figure 2, when ethanol is used as an octane number improver, the desired octane number (e.g., about 90) can be achieved at a lower mixing ratio than other octane number improvers (diisobutylene, cyclopentane, and toluene in Figure 2). Furthermore, ethanol has a high octane number improvement rate (so-called blending octane number) in the range where the mixing ratio is low. In addition to ethanol, a similar tendency is seen with alcohols such as propanol and butanol.

Figure 3 is a diagram for explaining the carbon strength of fuels, showing an example of the carbon strength when various fuels are used as vehicle fuel. As shown in Figure 3, the carbon strength of FT light naphtha, which is an e-fuel, is 1 g/mile, which is significantly lower than the carbon strength of 220 g/mile of gasoline derived from fossil fuels. In addition, the carbon strength of bioalcohol, for example bioethanol, is 73 to 161 g/mile, which is lower than the carbon strength of gasoline derived from fossil fuels, but higher than the carbon strength of FT light naphtha, which is an e-fuel.

Bioalcohol blended fuels, which are made by blending bioalcohol such as bioethanol with gasoline, are becoming popular worldwide as vehicle fuel. In particular, bioethanol blended fuels are widely used and therefore highly available. In this embodiment, a method for producing a gasoline alternative fuel is described, in which bioalcohol is mixed with and reformed using FT light naphtha, an e-fuel, as a base material to produce a gasoline alternative fuel with an octane number equivalent to gasoline and an extremely low carbon intensity.

Figure 4 is a diagram for explaining the difference in the octane number improvement effect depending on the composition of the base material, and shows, as an example, the mixing ratio of ethanol required to achieve an octane number of 90 (calculated by chemical reaction analysis). As shown in Figure 4, the mixing ratio of ethanol required to achieve an octane number of 90 increases as the octane number of the base material decreases, regardless of the composition of the base material. In addition, a base material containing aroma as a secondary component requires a higher mixing ratio of ethanol to achieve an octane number of 90 than a base material containing only paraffin as the main component. Furthermore, a base material containing olefin as a secondary component requires a higher mixing ratio of ethanol to achieve an octane number of 90 than a base material containing aroma as a secondary component. A similar tendency is seen with propanol and butanol. This is because olefins and aromas inhibit the octane number improvement effect of alcohols such as ethanol.

Figure 5 is a diagram for explaining the difference in carbon strength due to fuel composition, and shows the carbon strength of a fuel with an octane number of 90 as an example. As shown in Figures 2 and 5, the carbon strength of gasoline derived from fossil fuels is 220 g/mile. On the other hand, the carbon strength of a fuel made by mixing 69 vol% of an e-fuel base material with an octane number of 60 containing 85 vol% paraffin and 15 vol% olefin with 31 vol% bioethanol (derived from corn) is 50.6 g/mile. Furthermore, the carbon strength of a fuel made by mixing 79 vol% of an e-fuel base material with an octane number of 60 containing only paraffin with 21 vol% bioethanol (derived from corn) is 34.6 g/mile.

In this way, by reducing the content of olefins in the base material, which inhibit the octane number improving effect of alcohols such as ethanol, the mixing ratio of alcohol required to achieve an octane number of 90 can be reduced, and the carbon strength of the resulting fuel can be reduced. In the example of Figure 5, by reducing the olefin content of the base material from 15 vol% to 0 vol%, the carbon strength of the resulting fuel is reduced by approximately 32%, from 50.6 g/mile to 34.6 g/mile.

Olefins can be converted to paraffins (normal paraffins) by hydrogenation (cracking reaction). Hydrogenation of olefins to paraffins proceeds in the presence of a catalyst in which an active metal such as tungsten, iron, or nickel is supported on an acidic carrier such as silica or alumina, at high temperature (about 200 to 430°C), high pressure (about 70 to 210 kg/ ^cm2 ), and in a hydrogen stream. This reaction may be carried out in a fixed-bed reactor or a fluidized-bed reactor. Renewable hydrogen obtained by electrolysis of water using renewable electricity (Figure 1) can be used to hydrogenate olefins to paraffins, but additional energy input is required.

Figure 6 is a diagram for explaining the relationship between the olefin content of the substrate and the octane number improvement rate, and as an example, shows the octane number improvement rate (calculated by chemical reaction analysis) when 1 vol.% of ethanol is mixed into substrates with different olefin content rates. More specifically, the octane number improvement rate ((octane number after mixing with ethanol)/(octane number of substrate)) when ethanol is mixed into a substrate with an olefin content rate of 0 vol.% is set to "1", and the relative octane number improvement rate when the olefin content rate of the substrate is changed is shown.

As shown in FIG. 6, the higher the olefin content of the base material, the lower the octane number improvement rate due to the addition of ethanol, and the greater the rate of decrease in the octane number improvement rate. The rate of decrease in the octane number improvement rate increases as the olefin content of the base material increases, with an inflection point at around 10 vol.%. A similar tendency is seen with propanol and butanol. This tendency can also be confirmed by actual experimental results. Considering the effect of improving the octane number by adding alcohol such as ethanol, and the additional energy input required for hydrogenation, it is preferable to hydrogenate olefins to paraffins until the olefin content is at least 10 vol.% or less.

Furthermore, olefins have low oxidation stability, and the OICA (International Organization of Automobiles) gasoline standard (category 3 to 6) stipulates that the olefin content in vehicle fuel must be 10 vol% or less. Therefore, from the standpoint of the oxidation stability of the fuel, it is preferable to hydrogenate olefins to paraffins until the olefin content is at least 10 vol% or less.

Normal paraffin, which is also the main component of the base material FT light naphtha, precipitates heavy components at low temperatures (below about 5°C) (paraffin wax). Therefore, from the perspective of the low-temperature performance of the fuel, it is preferable to convert a portion of normal paraffin into isoparaffin, which is less likely to crystallize, through an isomerization reaction. When normal paraffin is isomerized into isoparaffin, the octane number of the entire base material increases depending on the isomerization ratio. The isomerization ratio from normal paraffin to isoparaffin is determined by the equipment specifications, the amount of energy that can be input, costs, etc.

Figure 7 is a diagram for explaining the blending octane number of alcohols. As an example, Figure 7 shows the blending octane number based on the results of chemical reaction calculations and actual measurement results when ethanol is mixed with a base material with an olefin content of 10 vol% and a different octane number. As shown in Figure 7, in the low range of the base material's octane number of about 50 to 100, the lower the octane number of the base material, the higher the octane number when ethanol is mixed. A similar tendency is seen with propanol and butanol.

FIG. 8 is a diagram for explaining the blending ratio of alcohol required to obtain a gasoline alternative fuel, and shows, as an example, the blending ratio of ethanol required to achieve an octane number of 90. In FIG. 8, the calculation result of the blending ratio b of ethanol calculated by the following formula (i) based on the blending octane number in FIG. 7 is shown by a black circle, and the experimental result is shown by a white circle. In the formula (i), (1-b) represents the blending ratio of the base material. As shown in FIG. 8, the blending ratio of ethanol required to achieve an octane number of 90 roughly coincides with the predicted value based on the blending octane number in FIG. 7 (solid line in FIG. 8).
(Base material octane number) x (Base material blend ratio) +
(Blending octane number) x (ethanol blend ratio) = (desired octane number)
(Base octane number) (1-b) + (Blending octane number) b = 90 ... (i)

The octane number of the base material (FT light naphtha) is around 60 to 70, so the blending ratio of ethanol is 30 vol% or less, as shown in Figure 8. Therefore, the content of base material (FT light naphtha) in the final gasoline alternative fuel obtained by blending ethanol with the base material will be 70 vol% or more. The same blending ratio (alcohol 30 vol% or less, base material (FT light naphtha) 70 vol% or more) will be obtained when blending alcohols such as propanol and butanol in addition to ethanol.

Figure 9 is a diagram for explaining the composition of a gasoline alternative fuel according to an embodiment of the present invention. As shown in Figure 9, FT light naphtha (base material) contains ovol% olefins along with normal paraffins as the main component. The olefin content ratio ovol% of the base material can be measured, for example, by analyzing the actual base material. After hydrogenation, in which a portion of the olefins ((100-α)vol% of olefins) are hydrogenated to normal paraffins, the base material contains oαvol% olefins. After further isomerization, in which a portion of the normal paraffins (ivol% of the entire base material) are isomerized to isoparaffins, the base material contains ivol% isoparaffins.

The final gasoline alternative fuel with the desired octane number (e.g., 90 octane number) contains b vol % bioalcohol (e.g., bioethanol) per 100 vol % of the base material after pretreatment (hydrogenation, isomerization). The mixing ratio b of bioalcohol to the base material can be calculated based on predetermined characteristics such as those shown in Figure 8. The octane number of the base material can be estimated by additive calculation based on the composition of the base material (carbon number distribution and olefin content ratio of normal paraffin) estimated according to the FT synthesis process or measured by analysis, and the isomerization ratio determined according to the equipment specifications, etc.

The olefin content of the final gasoline alternative fuel is (oα/(100+b)). From the viewpoint of the octane number improving effect by mixing bioalcohol and the oxidation stability of the fuel, it is preferable to determine the hydrogenation ratio α of the base material so as to satisfy the following formula (ii). Taking into consideration the balance with the input energy required for hydrogenating the base material and the decrease in octane number due to excessive hydrogenation, it is preferable to determine the hydrogenation ratio α so that, for example, both sides of the following formula (ii) are equal.
100oα/(100+b)≦10...(ii)

FIG. 10 is a diagram illustrating a method for producing a gasoline alternative fuel according to an embodiment of the present invention. As shown in FIG. 10, first, the olefin content ratio o of the base material is measured (step S1). Next, the octane number of the base material is calculated based on the olefin content ratio o of the base material measured in step S1 and the isomerization ratio i of the base material determined according to the equipment specifications, etc. (step S2). Next, based on the predetermined characteristics as shown in FIG. 8, an appropriate bioalcohol blending ratio b according to the octane number of the base material calculated in step S2 is calculated (step S3). More specifically, the octane number of the base material calculated in step S2, the blending octane number of the bioalcohol corresponding to the octane number of the base material as shown in FIG. 7, and the octane number to be achieved (for example, 90) are substituted into formula (i). Then, the equation of formula (i) is solved for the bioalcohol blending ratio b to calculate the bioalcohol blending ratio b and the base material blending ratio (1-b).
(Base material octane number) x (Base material blend ratio) +
(Blending octane number) x (bioalcohol blend ratio) = (desired octane number)
(Base octane number) (1-b) + (Blending octane number) b = 90 ... (i)

Next, based on the bioalcohol mixing ratio b calculated in step S3 and the olefin content ratio o of the base material measured in step S1, the hydrogenation ratio α in the base material is calculated so that the olefin content ratio of the gasoline alternative fuel is 10 vol% or less (step S4). Next, the base material containing olefins is hydrogenated according to the hydrogenation ratio α calculated in step S4 (step S5). Next, the base material hydrogenated in step S5 is further isomerized according to a predetermined isomerization ratio i (step S6). Next, bioalcohol is mixed with the base material isomerized in step S6 at the mixing ratio b calculated in step S3 (step S7). This completes the gasoline alternative fuel.

According to this embodiment, the following advantageous effects can be obtained.
(1) A method for producing a gasoline alternative fuel by mixing FT light naphtha (base material) obtained by FT synthesis using renewable electricity with bioalcohol obtained from biomass includes determining a mixing ratio b of bioalcohol to the base material based on the octane number of the base material, the blending octane number of the bioalcohol, and a predetermined target octane number (steps S1 to S3), determining a hydrogenation ratio α when hydrogenating olefins contained in the base material to paraffin based on the determined bioalcohol mixing ratio b and the olefin content ratio o of the base material so that the olefin content ratio (oα/(100+b)) of the gasoline alternative fuel is 10 vol% or less (step S4), hydrogenating the base material according to the determined hydrogenation ratio α (step S5), and mixing bioalcohol with the hydrogenated base material according to the determined bioalcohol mixing ratio b (step S7) (FIG. 10).

In this way, by using FT light naphtha, an e-fuel, as the base material and mixing it with bioalcohol in an appropriate ratio, it is possible to produce a gasoline alternative fuel with an octane number equivalent to that of gasoline and extremely low carbon intensity. In addition, by hydrogenating the base material and carrying out pre-processing to reduce the content of olefins that inhibit the effect of improving the octane number, it is possible to reduce the mixing ratio of bioalcohol required to achieve an octane number equivalent to that of gasoline, thereby further reducing the carbon intensity of the fuel (Figures 5 and 6).

(2) The method for producing a gasoline alternative fuel further includes isomerizing normal paraffins contained in the hydrogenated base material to isoparaffins (step S6) (FIG. 10). This improves the low-temperature performance of the fuel. In addition, isomerizing normal paraffins to isoparaffins improves the octane number, and the mixing ratio of bioalcohol required to achieve an octane number equivalent to that of gasoline is further reduced, thereby further reducing the carbon intensity of the fuel.

(3) The bioalcohol is any one of bioethanol, biopropanol, and biobutanol. For example, bioethanol, which is widely used and has high availability, can be used as an octane enhancer.

(4) The gasoline alternative fuel contains FT light naphtha (base material) derived from renewable energy and bioalcohol (Figures 1 and 9). The olefin content of the gasoline alternative fuel is 10 vol% or less. The bioalcohol content relative to the base material is determined based on the octane number of the base material, the blending octane number of the bioalcohol, and a predetermined target octane number. By setting the olefin content to 10 vol% or less, the bioalcohol content is minimized, making it possible to realize a gasoline alternative fuel with extremely low carbon intensity. Such a fuel also complies with gasoline standards for oxidation stability.

In the above embodiment, an example of FT synthesis using renewable hydrogen and carbon dioxide recovered from factory exhaust gas, etc., has been described in FIG. 1 etc., but FT synthesis using renewable electricity is not limited to this. For example, biomass, natural gas, coal, etc. may be used.

In the above embodiment, an example of obtaining FT light naphtha having a carbon number of about 6 to 10 from FT crude oil by fractional distillation is described in FIG. 1 etc., but the FT light naphtha obtained by FT synthesis is not limited to this. For example, the conditions of the FT synthesis process itself may be adapted so that FT light naphtha having a carbon number of about 6 to 10 is obtained. In this case, the fractional distillation step is not necessary.

In the above embodiment, an example in which the base material is isomerized and then bioalcohol is mixed therewith has been described with reference to FIG. 10 and the like, but the method for producing a gasoline alternative fuel is not limited to this.
For example, if the low temperature performance of the fuel is not a consideration, the isomerization step is not necessary.

The above description is merely an example, and the present invention is not limited to the above-mentioned embodiment and modifications, as long as the characteristics of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above-mentioned embodiment and modifications, and it is also possible to combine modifications together.

Claims (3)

A method for producing a gasoline alternative fuel by mixing FT light naphtha obtained by Fischer-Tropsch synthesis using renewable electricity and bioalcohol obtained from biomass,
Based on the octane number of the FT light naphtha, the blending octane number of the bioalcohol, and a predetermined target octane number, a mixing ratio of the bioalcohol to the FT light naphtha is determined;
Based on the determined mixing ratio of the bioalcohol and the olefin content ratio of the FT light naphtha, a hydrogenation ratio is determined when hydrogenating the olefins contained in the FT light naphtha into paraffins so that the olefin content ratio of the gasoline alternative fuel is 10 vol% or less;
Hydrogenating the FT light naphtha in accordance with the determined hydrogenation ratio;
A method for producing a gasoline alternative fuel, comprising mixing the hydrogenated FT light naphtha with the bioalcohol in accordance with the determined mixing ratio of the bioalcohol. 2. The method for producing a gasoline alternative fuel according to claim 1,
A method for producing a gasoline alternative fuel, further comprising isomerizing normal paraffins contained in the hydrogenated FT light naphtha to isoparaffins. 3. The method for producing a gasoline alternative fuel according to claim 1 or 2,
The method for producing a gasoline alternative fuel, wherein the bioalcohol is any one of bioethanol, biopropanol, and biobutanol.

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